Moved TLB Flush logic into privdec

pipelined/src/hazard/hazard.sv

@@ -60,6 +60,8 @@ module hazard(
   // A stage must stall if the next stage is stalled
   // If any stages are stalled, the first stage that isn't stalled must flush.
 
+  // *** can stalls be pushed into earlier stages (e.g. no stall after Decode?)
+
   assign StallFCause = CSRWritePendingDEM & ~(TrapM | RetM | BPPredWrongE);
   // stall in decode if instruction is a load/mul/csr dependent on previous
   assign StallDCause = (LoadStallD | StoreStallD | MDUStallD | CSRRdStallD | FPUStallD | FStallD) & ~(TrapM | RetM | BPPredWrongE);    

pipelined/src/privileged/privdec.sv

@@ -33,16 +33,18 @@
 
 module privdec (
   input  logic         clk, reset,
+  input  logic         StallM,
   input  logic [31:20] InstrM,
   input  logic         PrivilegedM, IllegalIEUInstrFaultM, IllegalCSRAccessM, IllegalFPUInstrM, 
   input  logic [1:0]   PrivilegeModeW, 
   input  logic         STATUS_TSR, STATUS_TVM, STATUS_TW,
   input  logic [1:0]   STATUS_FS,
-  output logic         IllegalInstrFaultM,
+  output logic         IllegalInstrFaultM, ITLBFlushF, DTLBFlushM,
   output logic         sretM, mretM, ecallM, ebreakM, wfiM, sfencevmaM);
 
   logic IllegalPrivilegedInstrM, IllegalOrDisabledFPUInstrM;
   logic WFITimeoutM;
+  logic       StallMQ;
 
   ///////////////////////////////////////////
   // Decode privileged instructions
@@ -65,7 +67,19 @@ module privdec (
     floprc #(`WFI_TIMEOUT_BIT+1) wficountreg(clk, reset, ~wfiM, WFICountPlus1, WFICount);  // count while in WFI
     assign WFITimeoutM = ((STATUS_TW & PrivilegeModeW != `M_MODE) | (`S_SUPPORTED & PrivilegeModeW == `U_MODE)) & WFICount[`WFI_TIMEOUT_BIT]; 
   end else assign WFITimeoutM = 0;
-  
+
+  ///////////////////////////////////////////
+  // sfence.vma causes TLB flushes
+  ///////////////////////////////////////////
+  // sets ITLBFlush to pulse for one cycle of the sfence.vma instruction
+  // In this instr we want to flush the tlb and then do a pagetable walk to update the itlb and continue the program.
+  // But we're still in the stalled sfence instruction, so if itlbflushf == sfencevmaM, tlbflush would never drop and 
+  // the tlbwrite would never take place after the pagetable walk. by adding in ~StallMQ, we are able to drop itlbflush 
+  // after a cycle AND pulse it for another cycle on any further back-to-back sfences. 
+  flopr #(1) StallMReg(.clk, .reset, .d(StallM), .q(StallMQ));
+  assign ITLBFlushF = sfencevmaM & ~StallMQ;
+  assign DTLBFlushM = sfencevmaM;
+
   ///////////////////////////////////////////
   // Fault on illegal instructions
   ///////////////////////////////////////////

pipelined/src/privileged/privileged.sv

@@ -100,11 +100,8 @@ module privileged (
   logic       STATUS_SPP, STATUS_TSR, STATUS_TW, STATUS_TVM;
   logic       STATUS_MIE, STATUS_SIE;
   logic [11:0] MIP_REGW, MIE_REGW;
-  logic       StallMQ;
-  logic WFITimeoutM; 
   logic [1:0] NextPrivilegeModeM;
 
-
   ///////////////////////////////////////////
   // track the current privilege level
   ///////////////////////////////////////////
@@ -116,9 +113,10 @@ module privileged (
   // decode privileged instructions
   ///////////////////////////////////////////
 
-   privdec pmd(.clk, .reset, .InstrM(InstrM[31:20]), 
+   privdec pmd(.clk, .reset, .StallM, .InstrM(InstrM[31:20]), 
               .PrivilegedM, .IllegalIEUInstrFaultM, .IllegalCSRAccessM, .IllegalFPUInstrM, 
               .PrivilegeModeW, .STATUS_TSR, .STATUS_TVM, .STATUS_TW, .STATUS_FS, .IllegalInstrFaultM, 
+              .ITLBFlushF, .DTLBFlushM,
               .sretM, .mretM, .ecallM, .ebreakM, .wfiM, .sfencevmaM);
 
   ///////////////////////////////////////////
@@ -158,15 +156,6 @@ module privileged (
   assign BreakpointFaultM = ebreakM; // could have other causes too
   assign EcallFaultM = ecallM;
 
-  flopr #(1) StallMReg(.clk, .reset, .d(StallM), .q(StallMQ));
-  assign ITLBFlushF = sfencevmaM & ~StallMQ;
-  assign DTLBFlushM = sfencevmaM;
-  // sets ITLBFlush to pulse for one cycle of the sfence.vma instruction
-  // In this instr we want to flush the tlb and then do a pagetable walk to update the itlb and continue the program.
-  // But we're still in the stalled sfence instruction, so if itlbflushf == sfencevmaM, tlbflush would never drop and 
-  // the tlbwrite would never take place after the pagetable walk. by adding in ~StallMQ, we are able to drop itlbflush 
-  // after a cycle AND pulse it for another cycle on any further back-to-back sfences. 
-
 
   // A page fault might occur because of insufficient privilege during a TLB
   // lookup or a improperly formatted page table during walking